Volcanism in the Mount Taylor Region, New Mexico L

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Volcanism in the Mount Taylor region, New Mexico L. S. Crumpler, 1982, pp. 291-298 in: Albuquerque Country II, Wells, S. G.; Grambling, J. A.; Callender, J. F.; [eds.], New Mexico Geological Society 33rd Annual Fall Field Conference Guidebook, 370 p.

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VOLCANISM IN THE MOUNT TAYLOR REGION

L. S. CRUMPLER Department of Planetary Sciences University of Arizona Tucson, Arizona 85721

INTRODUCTION Mount Taylor and its adjoining field of late Cenozoic cones am domes, Mesa Chivato, are prominent features on the western horizoi of Albuquerque (fig. 1). The purpose of this paper is to synthesize ou current knowledge about volcanism in the Mount Taylor region. Volcanic fields occur intermittently along the margin of the Colorad( Plateau, and locally, it is difficult to categorically define where on volcanic field ends and another begins. In this review the Mount Taylo region shall be defined as a region bounded on the east by Mesa PrieL in the Rio Puerco valley, on the west by the Bandera volcanic field on the north by Cabezon Peak volcanic neck, and on the south by Zun Salt Lake (fig. 2). The Mount Taylor "field" encompasses Pliocene Pleistocene basalts and differentiated rocks capping high mesas at th( foot of the Mount Taylor composite volcano and adjacent high mesas The Mount Taylor region includes the collective areas of volcanisn overshadowed by Mount Taylor, such as the volcanism in the Bander area of the Zuni Mountains and the young McCartys lava flow (se( Maxwell, this guidebook). OVERVIEW OF VOLCANISM Volcanism in the Mount Taylor region is similar to that occurrinl elsewhere along the boundary between the Colorado Plateau and the Basin and Range province (see Laughlin and others, this guidebook) Mount Taylor is similar in many respects to the other large composite "andesitic" volcanoes along the periphery of the Colorado Plateau. I forms a composite accumulation of rhyolite, trachyte, alkali andesite and other mafic rocks erupted in late Cenozoic time, and it is surroundec by fields of older and younger monogenetic, dominantly basaltic cinde] cones and flows. Volcanism throughout the Mount Taylor region appears to have occurred over the last 4 m.y. (Table 1), or 7 m.y. if Mesa Gallina, southeasi of Mount Taylor, is included. A histogram of all available dates (fig. 3) reveals that the bulk of the dated flows lie in the 3.5 m.y. to 2.( my. range. The increased number of flows younger than 500,000 year may reflect a sampling bias toward younger flows. Some of the oldest activity recognized in the region includes trachyte and rhyolite dome-building eruptions, which initiated volcanism at the present site of Mount Taylor (Bassett and others, 1963; Lipman am others, 1978). Rhyolite ash and pumice underlie many of the oldesi basalts capping high mesas around Mount Taylor, and they have beer found beneath the lowest flow units as far north as the northern end ol Mesa Chivato.

Most of the radiometric dates are concentrated in the area immediately surrounding Mount Taylor and little is known about the chronology of basalts to the southeast of Mount Taylor (however, see Baldridge, road- log segment II-B, this guidebook). One basalt flow in the Lucero Mesa area (Carrizo Mesa) was dated at 3.5 my. (Bachman and Mehnert, 1978). Younger basaltic activity is widely dispersed south of Mount Taylor. This includes the Laguna basalt flow, El Tintero flow west of Grants, McCartys basalt flow, and the Bandera area in the southern Zuni Moun- tains area, all of which are in the 500,000-1,000 year age range. Many of the vents for basalts in the region show linear alignment indicative of control by dominating northeasterly and west-northwest- erly basement structures (see Laughlin and others, this guidebook). In the northern part of the Mount Taylor field (Mesa Chivato), surface faults follow several northeastward-trending fissure vents and formed subsequent to fissure volcanism. The reverse is also true; thus, showing the complex relationship that exists between recent structural move- ments and basaltic volcanism in the region (Crumpler, 1980). Similarly, several vents in the Bandera area are closely related to faulting, such as the Paxton Springs and Cerro Colorado vents which erupted in structurally-controlled canyons within the Zuni Mountains (Laughlin and others, 1972b). Both of these vents occur in the Precambrian crystalline terrane of the Zuni Mountains. The overall northeasterly alignment of the Mount Taylor and Bandera areas with the Jemez, Raton, White Mountain, and Pinacate fields has

VOLCANISM 293 suggested to some researchers that a major continental northeast-trend- field. Laughlin and others (19726) estimate that this flow is older than ing basement weakness has played a part in controlling the location of the McCartys flow but younger than the flow which is directly overlain the volcanism (Mayo, 1958; Laughlin and others, 1972b; Laughlin and by the McCartys near its terminus (i.e., <188,000 years). others, this guidebook). It has been suggested that this lineament rep- The Zuni Salt Lake crater, 80 km southwest of the Bandera field, is resents a hot-spot trace (Suppe and others, 1975). However, the local a young maar-type vent in which many primary morphologic features age of eruptions appears to be randomly distributed along the lineament of typical maars are preserved (Bradbury, 1967; Cummings, 1968; (Lipman and Mehnert, 1975), and this does not support the simple age Aubele and others, 1976). It is unusual, however, in that it has cinder progression model normally attributed to moving hot spots. cones built on its floor. In fact, the Zuni Salt Lake maar is the type The Bandera field is situated on the southern edge of the Zuni Uplift; locality for this type of maar. whereas, the Mount Taylor field lies on the Acoma Sag. Although Somewhat older, but still preserving many primary flow features, is volcanism on uplifted terrain is not uncommon, volcanism situated on the tholeiitic El Tintero cone and flows west of Grants (Thaden and sags is more anomalous. The Mount Taylor field is anomalous in other Ostling, 1967; Lipman and Moench, 1972). Another older tholeiite flow respects, including extreme Tia, enrichment of early basaltic rocks and (370,000 years) fills the Rio San Jose valley near the site of Laguna overall similarity of its volcanism with oceanic aseismic volcanism. Pueblo (Moench, 1963a, b; Schlee and Moench, 1963a, b; Lipman and Any simple explanation of the sag-volcanism relationship at Mount Moench, 1972), where it was responsible for stagnating the flow of the Taylor must address these unique characteristics. Rio San Jose and creating the cienega there. The location of the vent for this flow has not been determined. LATE QUATERNARY ERUPTIONS Other relatively recent eruptions occur 25 km south of Mesita and The tholeiitic McCartys lava flow is one of the most voluminous 1-40 (Moench, 1964) and include the Cerro Verde lava cone and Cerro recent flows in the world. Its youthful "malpais" topography assured Colorado cinder cone. The primary pressure-ridge type topography of its recognition by non-scientists and scientists alike, and, as a landmark, the Cerro Verde flows is preserved locally. Judging from other flows it has figured in tales of gold and fictional adventures of cowboys of similar preservation that have been dated, it may be the result of an (Dobie, 1967; L'amour, 1960). Several studies and maps have encom- eruption on the order of 200,000 to 400,000 years ago; however, little passed at least parts of the flow (Nichols, 1946; Kuiper and others, is known about the volcanism of this area (Kelley and Wood, 1946; 1966; Thaden and others, 1967a; Renault, 1970; Leeman, 1970; Hathe- Jicha, 1958). way, 1971; Laughlin and others, 19726; Lipman and Moench, 1972; Carden and Laughlin, 1974; and Maxwell, this guidebook). The total volume of the McCartys flow is about 7 km' (Williams and LATE TERTIARY AND EARLY QUATERNARY McBirney, 1979); this compares with the eruption of the Laki fissure VOLCANISM OF THE MOUNT TAYLOR FIELD of Iceland in 1783 which poured out 12 km' of basalt. From its source All of the eruptions discussed in the section above lie at or near the at an inconspicuous vent 40 km south of 1-40, to its terminus near the present drainage levels, and even without radiometric-age evidence their village of McCartys in the Rio San Jose valley, it flowed along a broad positions in present valley bottoms attest to their relative youth. In valley confined by cliffs of Zuni Sandstone on the east and along the terms of volume and numbers of vents, most of the volcanism in the margin of an older flow (30, Table 1) of similar volume and extent on Mount Taylor region is much older, and many older flows cap mesas the west. that stand 100 to 500 m above present drainages. Dates indicate that The age of the McCartys flow is not well established. The flow existed the highest levels around Mount Taylor represent the regional land at the time of the Coronado expedition in 1540. The expedition followed surface approximately 2.5 my. ago (Bachman and Mehnert, 1978; a well-traveled Indian trail across it, but whether ancestors of the Pueblo Armstrong and others, 1976). Therefore, erosional down-cutting must Indians witnessed its eruption is not clear. Darton (1915) cited local have been extreme in the interval between about 2.5 my. and 500,000 Indian legends of a river of fire in the Rio San Jose valley that had yrs in order to account for the difference in the elevation of high mesa buried fields cultivated by their ancestors. Other legends speak of the basalts and flows in the valley floors (see Grimm, road log segment II- "year of fires" (Navajo mythology holds that the flow is the congealed B).There is some evidence that later flows erupted onto Mesa Chivato blood of Big Monster, killed by the War Twins on Mount Taylor; see but subsequently cascaded to lower levels (Crumpler, 1980), suggesting Reichard, 1974). The archeologic date of 700 A.D. given by Nichols that erosion began to isolate high mesas even while eruptions were still (1946) is based on the observation that the flow overlies alluvium similar continuing in high-mesa fields. to that several kilometers farther down the valley in which pottery These observations demonstrate that immense quantities of rock have fragments from Pueblo I period were found. The correlation of the been removed in geologically short periods of time. This can be ob- alluvium is doubtful, but an age of 1,300 years seems reasonable con- served by standing on the western rim of Mesa Chivato and looking sidering the lack of erosion and bioturbation. Only a few recent gen- out over the desert floor, some 500 m below. Only after some tens of erations of trees and their associated root systems have caused wedging kilometers can one see mesas of equivalent height. This erosion has and disruption of surface slabs on the pahoehoe crust; therefore, pffion exposed the internal, intrusive structures of cinder cones, fissures, and and juniper vegetation has been established recently. maars in the Rio Puerco valley, between the Mount Taylor field and The Bandera field on the western side of the Mount Taylor region is Mesa Prieta, to form the Rio Puerco volcanic necks. The Rio Puerco a relatively young complex of cinder and spatter cones and associated necks are among the most concentrated and best exposed examples of flows of both alkalic and tholeiitic affinities. Bandera-crater cinder cone volcanic necks in the world. Aside from early reconnaissance by Dutton and adjacent lava tubes and ice caves are the most prominent landmarks (1885), Johnson (1907), and Hunt (1938) and recent petrochemical of the area. The extensive network of lava tubes was documented by studies (Brunton, 1952; Brown, 1968; Brown and Kudo, 1969; Kudo Hatheway and Herring (1970) and Hatheway (1971), whereas Laughlin and others, 1972), the Rio Puerco necks have received little attention. and others (1971) and Causey (1971) reported on the petrology and However, they provide instructive examples of the internal structure chemistry of basalts and ultramafic inclusions of the field. The recent and dynamics of cinder cones, feeder dikes, and maars. flow, which emerged from Zuni Canyon and flowed into the valley Some of the Rio Puerco necks are relatively simple feeder dikes or immediately south of Grants, is from the Cerro Colorado vent, one of two centers which erupted within the Zuni Mountains in the Bandera 294 CRUMPLER monolithic accumulations of homogeneous basalt, jointed with classic PETROLOGY AND ISOTOPIC DATA sweeping columnar structure. Cabezon Peak is a good example of this Figures 6 through 9 are summaries of all available petrochemical and simple form. Although impressive in size, it is relatively devoid of the isotopic data for the Mount Taylor region. For detailed discussions of more complex structures. these and other data, the interested reader is referred to the appropriate A natural cross-section of a vent can be seen along the edge of Mesa references cited below. Chivato, exposed on the East Grants Ridge (Bassett and others, 1963; The alkalies-silica plot of Figure 6 indicates that many of the youngest see road-log segment II-B). An oblique section occurs at Cubero volcano eruptions are tholeiitic; whereas, the oldest volcanoes are strongly al- on 1-40 near the village of Cubero. Here, the relationship between cone kalic. The mafic rocks of the Mount Taylor volcano are more alkalic and the underlying basaltic plug is one in which the massive plug gives than the more silicic rocks of the main cone-building stage. way upward to numerous dikelets, which in turn invade and complexly One of the unusual aspects of the basanites (high nepheline-normative intertwine among the cinders at the core of the cone. basalts) not shown here is their exotic TiO2 content. Several samples There are a few volcanic necks and dissected cinder cones exposed exceed 3.5 percent TiO2, and a few basanites (Lipman and Moench, on the western side of Mesa Chivato in the drainage of the Arroyo 1972; Crumpler, 1977) exceed 4 and 5 percent TiO,. This high TiO, Chico, but these are even more poorly known due to the difficulty of content is seen in few terrestrial lavas, the highest TiO, typically being access. Cerro Alesna ("awl") is a particularly fine example of a neck that of oceanic, alkalic suites (-3.5 percent). showing sweeping columnar structure. Compiling all of the alkalic rocks of the Mount Taylor field on a Mesa Chivato, the broad plateau extending northeastward from the standard AMF plot (fig. 7) results in a classic alkalic-suite trend, with base of Mount Taylor, is the site of an incredible array of fissure vents, the exception of the dacitic and andesitic rocks which appear to have collapse (pit) craters, maars, and trachyte domes (Aubele and others, no mafic, subalkalic counterparts. A distinct gap occurs in compositions 1976; Crumpler, 1980). In fact, the greatest concentration of individual between hawaiite and mugearite which Crumpler (1980) had originally vents in the Mount Taylor region occurs in this area. In addition to interpreted as a sampling problem. However, this compilation indicates morphologic diversity, Mesa Chivato exposes a rare oceanic-type alkalic that the gap is real. The rhyolites, dacites, and andesites are separate volcanic suite ranging from basanite through trachyte in a sequence in from the true alkalic lineage. The intermediate position of the andesites which basalt was extruded first and trachyte domes were extruded last. and the dacites between rhyolite, which Baker and Ridley (1970) in- The few dates available from the area (17, 20, 21, 26, Table 1) indicate dicated may be anatectic melting products, and trachytes, which Crum- that volcanism on Mesa Chivato occurred from about 3.2 to 1.5 my. pler (1980) argued were the results of fractional crystallization, suggests ago. The abundance of maars in the region indicates that the climate that mixing of both end members may have occurred to generate the of that time was an extremely wet one. observed intermediate andesitic to dacitic rocks. Dacites and andesites The geology of Mount Taylor itself is poorly understood. Aside from of the Mount Taylor complex have strong alkalic affinities and are not the work of Hunt (1938), only petrochemical studies (Baker and Ridley, of strict calc-alkalic parentage. They are not true andesites or dacites 1971) had taken place until 1978, when Lipman and others (1978) of the island-arc type, either. mapped the Mount Taylor quadrangle and Crumpler (1978) mapped the This interpretation of the dacites as the product of magma mixing is northern and western flanks. The results of these two mapping projects supported by the strontium-isotopic data (Table 2 and fig. 8). A granite are compiled in Figures 4 and 5. The main cone is not as eroded as xenolith in rhyolite pumice yielded an "Sr/"Sr value of 0.9193, and a was previously thought. The margins of many of the more silicic flows dacite sample value is 0.7193 suggesting the probability of contami- are still intact locally, as are numerous pyroclastic flows and mud flows. nation of mantle-derived magmas with crustal melts to form dacitic Central volcanism commenced between 4.3 and 3.3 my. ago with products. Contamination of other rocks in the field, including the an- the eruption of trachyte and rhyolite domes and basanite flows. These desitic rocks of Mount Taylor, appears less probable (fig. 9) as the lavas were followed by increasingly "andesitic" or porphyritic rocks of in- with the highest strontium content tend to have the highest radiogenic- termediate composition which were responsible for the cone-building strontium contents. This is the inverse of what would be expected for activity. At the same time, alkali basalts (some bearing lherzolite and a contamination origin of the high ratios. This tendency appears in pyroxenite nodules) were erupted high on the flanks together with some several alkalic suites throughout the world, and it has not been satis- alkalic differentiates (mugearite and benmorite). Mud flows began to factorily explained. build an extensive apron around the main cone. Most of the andesitic flows overlie the most voluminous volcanoclastic debris, and it is prob- CONCLUSIONS able that an early cone had been destroyed by explosion to yield some of this extensive volume of debris. Volcanism culminated with the The following is a summary of the salient points based on a survey injection of a radial dike swarm in the interior of the main cone, and of what is now known about volcanism in the Mount Taylor region. these dikes are now visible in the erosional amphitheater. This phase 1. Volcanism appears to have occurred from about 4 m.y. ago to the probably was allied closely with the extrusion of dacitic domes and present. flows high up on the flank of the main cone. Several pyroclastic flows 2. Up to 500 m of rock were eroded, over a broad region, in as little which swept down the flanks of the cone duirng this latest activity have as 3 million years after initial volcanism. been dated at around 2.5 my. (22, 23, 24, Table 1). Altogether, the 3. The youngest flows are dominantly tholeiitic and the oldest flows formation of Mount Taylor took between one and two million years. are alkalic. A complete alkalic suite was erupted in the Mount The erosional amphitheater which opens out to the east to form Water Taylor field. Some of the alkali basalts contain over 4 percent Canyon is similar to that seen in the San Francisco Mountain composite TiO2. The chemical character of the Mount Taylor field lavas is cone of Arizona, and both bear a suspicious resemblance to the crater oceanic. of Mount St. Helens. It is possible that both Mount Taylor and San 4. Orientation of volcanic vents in the region was strongly controlled Francisco Mountain owe the existence of their interior valleys to a late by regional northeasterly (and, to a lesser extent, west-northwest- stage eruption similar to that of Mount St. Helens. The abundant vol- erly) faults involving crystalline basement rocks. canoclastic debris now capping the walls of Water Canyon may in part 5. Mount Taylor is the result of 2 million years of eruption of alkalic be the remains of a similar lateral blast eruption, affected by two million mafic, intermediate, and probably anatectic rhyolitic lavas. The years of erosion. last activity occurred 2.5 m.y. ago.

VOLCANISM 297

Baker, I. and Ridley, W. I., 1970, Field evidence and K, Rb, Sr data bearing on the origin of the Mount Taylor volcanic field, New Mexico, U.S.A.: Earth and Planetary Science Letters, v. 10, P. 106-114. Bassett, W. A., Kerr, P. F., Schaeffer, 0. A., and Stoenner, R. W., 1963, Potassium-argon ages of volcanic rocks near Grants, New Mexico: Geological Society of America Bulletin, v. 74, p. 221-226. Bradbury, J. P., 1967, Origin, paleolimnology, and limnology of Zuni Salt Lake maar, west-central New Mexico (Ph.D. thesis): University of New Mexico, Albuquerque, 247 p. Brookins, D. G., Crumpler, L. S., and Elston, W. E., 1977, Sr isotopic initial ratios from the Mount Taylor volcanic field, New Mexico: Isochron/West, n. 21, p. 18. Brown, W. T., 1968, Igneous geology of the Puerco necks, Sandoval and Valen- cia counties, New Mexico (M.S. thesis): University of New Mexico, Albu- querque, 89 p. Brown, W. T. and Kudo, A. M., 1969, Inclusions of ultramafic and sedimentary rock in volcanic necks, New Mexico: Geological Society of American Ab- stracts with Programs, v. 5, p. 10. Brunton, G. D., 1952, The study of an unusual augite near Cabezon Peak, Sandoval County, New Mexico (M.S. thesis): University of New Mexico, Albuquerque, 40 p. Carden, J. R. and Laughlin, A. W., 1974, Petrochemical variations in the McCartys basalt flow, Valencia County, New Mexico: Geological Society of American Bulletin, v. 85, p. 1479-1484. Causey, J. D., 1971, Geology, geochemistry, and lava tubes in Quaternary basalts, northern part of Zuni lava field, Valencia County, New Mexico (M.S. thesis): University of New Mexico, Albuquerque, 57 p. Crumpler, L. 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